Omnidirectional retrodirective antenna



Jan. 14, 1969 A. E. MARSTON 3,422,436

OMNIDIRECTIONAL RETRODIRECTIVE ANTENNA Filed Jan. 17, 1966 mpmsms PLANEPHASE FRONT"' \J CIRGULATOR INVENTOR ARTHUR E. MARSTON BY M ATTORNEY3,422,436 OMNIDIRECTIONAL RETRODIRECTIVE ANTENNA Arthur E. Marston,Alexandria, Va., assignor to the United States of America as representedby the Secretary of the Navy Filed Jan. 17, 1966, Ser. No. 521,220 [1.5.Cl. 343-754 Int. Cl. H01q 19/06; H01q 13/00; H0111 3/26 8 ClaimsABSTRACT OF THE DISCLOSURE The present invention relates generally toimprovements in retrodirective antennas and the like and moreparticularly to new and improved retrodirective antennas whereby asignal can be received from any direction and re-radiated back in thatdirection to the exclusion of all other directions.

In the field of retrodirective antennas and reflectors it has been thegeneral practice to employ devices which are passive, such as Luneberglenses or corner reflectors, to reradiate received signals back in thedirection from which they came. Where it has been desired to amplify thereradiated signal, to shift its frequency, or to impress someintelligence on it, the device has generally taken the form of anantenna having wide-angle scanning properties. Although such deviceshave served the purpose they have not proved entirely satisfactory underall conditions of service for the reasons that such devices do notoperate over all 360 in azimuth, and are not capable of receiving asignal from any direction and reradiating that signal back toward thedirection from which the signal originated, to the exclusion of allother directions.

The general purpose of this invention is to provide a retrodirectiveantenna which embraces all of the advantages of similarly employed priorart devices and possesses none of the aforedescribed disadvantages. Toattain this the present invention contemplates a unique arrangement ofthree-port circulators, electromagnetic energy refraction devices, suchas Luneberg lenses, and a circular focusing antenna array, whereby asignal can be received from any direction in azimuth and reradiated backexclusively in the direction from which it came, and whereby the signalcan be received and reradiated with a receiving and transmitting gaincomparable to the gain of a focusing antenna of similar physicaldimensions. The present invention also provides for a true antenna asopposed to a passive reflector, thus allowing the impression ofintelligence on the reradiated signal.

An object of the present invention is the provision of a retrodirectiveantenna capable of receiving signals from all 360 in azimuth.

Another object is to provide such a device that will reradiate a signalreceived from any direction in azimuth back in that direction only.

A further object of the invention is the provision of an omnidirectionalretrodirective antenna which will nited States Patent F 3,422,436Registered Jan. 14, 1969 ice receive and transmit with a gain comparableto the gain of a focusing antenna of similar physical dimensions.

Still another object is to provide a retrodirective antenna which iscapable of receiving signals from any direction in azimuth and whichwill reradiate the signal back exclusively in the direction from whichthe signal originated while beng able to impress intelligence on thereradated signal.

Other objects and features of the invention will become apparent tothose skilled in the art as the disclosure is made in the followingdescription of a preferred embodiment of the invention as illustrated inthe accompanying sheet of drawing in which:

The figure shOWs a perspective view of one embodiment of the inventionwith some electrical connections not shown for the purpose of clarity.

Referring now to the drawing there is shown in the figure a completecircular ring 4 of receiving and radiating focusing elements, such aswave-guide horns, some of which elements are designated as 5-9 and15-19. Each of the elements in the ring 4 is electrically connected toone port of a three-port circulator, as exemplified in the figure by theconnections between elements 5-9 and circulators 21-25, and betweenelements 15-19 and circulators 27-31, respectively.

Each of the circulators, in turn, is electrically connected, by means ofits remaining two ports, to two stacked Lune-berg lenses 35 and 36, eachof which has a diameter equal to the diameter of the ring 4.

As exemplified in the figure, circulators 21-25 and 27-31 areelectrically connected to Luneberg lens 35 by means of ports 5'-9' andby means of ports 15'-19', respectively, and circulators 21-25 and 27-31are electrically connected to Luneberg lens 36 by means of ports 5"-9"and 15-19", respectively. The electrical lengths of the connectionsbetween each of the receiving and radiating focusing elements and theirrespective circulators must be uniform with respect to each other, asmust be the electrical lengths between each circulator and each Luneberglens.

In the operation of the retrodirective antenna, an electromagnetic waveis received, for example, by the receiving and radiating elements 15-19,and the energy from this incident wave is routed from each focusingelement 15-19 through equal-length electrical connections, tocirculators 27-31, respectively. The energy is then directed, bycirculators 27-31, through another set of equal-length electricalconnections to the lower Luneberg lens 36. A Luneberg lens, e.g., lens36, has the property that when energy from a plane wave is incident andis received by the ports 1 5"-19", the energy is focused down to a port7" on the opposite side of the lens 36. The energy then exits from port7" and is routed by circulator 23 upwards to the upper lens 35 and toport 7', where the energy is reformed by the action of lens 35 into awave which exits the lens 35 at ports 15'-19'. The energy of this waveis then routed through equal-length electrical connections tocirculators 27-31, which in turn, direct the energy through equallengthelectrical connections to radiating elements 15-19, respectively. Theenergy then leaves the antenna, as a plane wave, aimed back exclusivelyin the direction of incidence. It is obvious, from the circular symmetryof the antenna, that this will work for all angles of arrival, and it isalso apparent that because the received signal is transmitted throughtransmission lines it is possible to impress a piece of intelligenceupon that signal if it so desired.

It can, therefore, be seen that the invention very efiectively providesan omnidirectional retrodirective antenna which can receive a signalfrom any direction in azimuth and which can reradiate that signal, or amodified form of that signal, back exclusively in the direction fromwhich the signal originated. This can be accomplished while providing apower gain comparable to that achieved by a focusing antenna of similarphysical dimensions.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and thatnumerous modifications or alterations may be made therein withoutdeparting from the spirit and the scope of the invention as set forth inthe appended claims.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. In an omnidirectional, retrodirective antenna, the combinationcomprising:

receiving and radiating elements,

first and second signal delay means each having a plurality of portsconnected thereto and being equal in number to the number of receivingand radiating elements,

a plurality of nonreciprocal switches,

each of said receiving and radiating elements being connected to arespective port on each delay means by a separate nonreciprocal switchto direct received signals sequentially through both delay means andthen back to the same elements at which the signals were received forreradiation.

2. The combination of claim 1 wherein said receiving and radiatingelements comprise wave-guide horns.

3. The combination of claim 1 wherein said receiving and radiatingelements are oriented in a complete circular ring.

4. The combination of claim 3 wherein said first and second delay meanseach comprise a circular Luneberg lens.

5. The combination of claim 4 wherein the diameter of each of saidLuneberg lenses is equal to the diameter of said circular ring.

6. The combination of claim 1 wherein said nonreciprocal switches arethree-port circulators.

7. The combination of claim 6 wherein each of said receiving andradiating elements is connected to its respective circulator byequal-length electrical connections 8. The combination of claim 7wherein each of said circulators is connected to said refraction meansby equal-length electrical connections.

References Cited UNITED STATES PATENTS 3,170,158 2/1965 Rotman 3437533,230,536 1/1966 Cheston -a 343-754 3,259,902 7/1966 Malech 3437533,354,461 11/1967 Kelleher 343-854 ELI LIEBERMAN, Primary Examiner.

US. Cl. X.R. 343-777, 854

